The compound, 1-(carbazol-4-yloxy-3-[[2-(o-methoxyphenoxy)ethyl]-amino]-2-propanol is known as Carvedilol. Carvedilol is depicted by the following chemical structure:

Carvedilol is disclosed in U.S. Pat. No. 4,503,067 to Wiedemann et al. (i.e., assigned to Boehringer Mannheim, GmbH, Mannheim-Waldhof, Fed. Rep. of Germany), which was issued on Mar. 5, 1985.
Currently, Carvedilol is synthesized as free base for incorporation in medication that is available commercially. The aforementioned free base form of Carvedilol is a racemic mixture of R(+) and S(−) enantiomers, where nonselective β-adrenoreceptor blocking activity is exhibited by the S(−) enantiomer and α-adrenergic blocking activity is exhibited by both R(+) and S(−) enantiomers. Those unique features or characteristics associated with such a racemic Carvedilol mixture contributes to two complementary pharmacologic actions: i.e., mixed venous and arterial vasodilation and non-cardioselective, beta-adrenergic blockade.
Carvedilol is used for treatment of hypertension, congestive heart failure and angina. The currently commercially available carvedilol product is a conventional, tablet prescribed as a twice-a-day medication in the United States.
Carvedilol contains an α-hydroxyl secondary amine functional group, which has a pKa of 7.8. Carvedilol exhibits predictable solubility behaviour in neutral or alkaline media, i.e. above a pH of 9.0, the solubility of carvedilol is relatively low (<1 μg/mL). The solubility of carvedilol increases with decreasing pH and reaches a plateau near pH=5, i.e. where saturation solubility is about 23 μg/mL at pH 7 and about 100 μg/mL at pH=5 at room temperature. At lower pH values (i.e., at a pH of 1 to 4 in various buffer systems), solubility of carvedilol is limited by the solubility of its protonated form or its corresponding salt formed in-situ. The hydrochloride salt of carvedilol generated in-situ in an acidic medium, such as in a simulated gastric fluid, is less soluble in such medium than the protonated form of carvedilol.
In light of the foregoing, a salt, and/or novel crystalline form of carvedilol (i.e., such as carvedilol hydrobromide monohydrate, carvedilol hydrobromide anhydrate, and/or other solvates thereof) with greater aqueous solubility, chemical stability, etc. would offer many potential benefits for provision of medicinal products containing the drug carvedilol. Such benefits would include products with the ability to achieve desired or prolonged drug levels in a systemic system by sustaining absorption along the gastrointestinal tract of mammals (i.e., such as humans), particularly in regions of neutral pH, where a drug, such as carvedilol, has minimal solubility.
Surprisingly, it has now been shown that a novel crystalline form of carvedilol hydrobromide salt, can be isolated as a pure, crystalline solid, which exhibits much higher aqueous solubility than the corresponding free base or other prepared crystalline salts of carvedilol, such as the hydrochloride salt. This novel crystalline form also has potential to improve the stability of carvedilol in formulations due to the fact that the secondary amine functional group attached to the carvedilol core structure, a moiety pivotal to degradation processes, is protonated as a salt.
In light of the above, a need exists to develop different carvedilol forms and/or different compositions respectively, which have greater aqueous solubility, chemical stability, sustained or prolonged drug or absorption levels (i.e., such as in neutral gastrointestinal tract pH regions, etc.).
There also exists a need to develop methods of treatment for hypertension, congestive heart failure or angina, etc. which comprises administration of the aforementioned compounds and/or compositions.
The present invention is directed to overcoming these and other problems encountered in the art.